remote building and propagation of substituters/trusted-public-keys?

[colemickens]

I'm looking at removing almost all of my "nix wrapper" script in favor of nix-fast-build.

One other thing that my wrapper script does is re-specify substituters and trusted-public-keys and ensure that the remote build is performed with them.

1. Does nix-fast-build do this? (If so, I can send a PR noting it in the README in the remote builder section)
2. If not, does it make sense to add such a feature?
3. (I wonder if nix has or should have a feature to print the net of global and user nix conf and use that?)